Stents, grafts, stent-grafts, vena cava filters, and similar implantable medical devices, collectively referred to hereinafter as stents, are radially expandable endoprostheses which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. Stents may be implanted in a variety of body lumens or vessels such as within the vascular system, urinary tracts, bile ducts, fallopian tubes, coronary vessels, peripheral or secondary vessels, etc.
Stents may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system in order to maintain vascular patency and thus reduce the likelihood of thrombosis and restenosis which may occur after the procedure, requiring another angioplasty procedure or a surgical bypass operation.
Stents are expandable frameworks, usually cylindrical or tubular in shape, functioning to physically hold open, and if desired, to expand the wall of a vessel lumen. One common design is stents formed of a series of circumferential bands, each band formed of interconnected stent struts. Typically, stents are radially compressed or crimped for insertion through small body lumens via catheter assemblies, and are then expanded to a larger diameter once at the treatment site. Stents come in a variety of configurations and may be self-expanding, expanded by an internal radial force, such as when mounted on a balloon, or a combination of self-expanding and balloon expandable (hybrid expandable).
Of the many problems that may be addressed through stent-based local delivery of beneficial agents, one of the most important is restenosis. Restenosis is a major complication that can arise following vascular interventions such as angioplasty and the implantation of stents. Simply defined, restenosis is a wound healing process that reduces the vessel lumen diameter by extracellular matrix deposition, neointimal hyperplasia, and vascular smooth muscle cell proliferation, and which may ultimately result in renarrowing or even reocclusion of the lumen. To treat this condition, additional revascularization procedures are frequently required, thereby increasing trauma and risk to the patient.
One of the techniques recently introduced to address the problem of restenosis is the use of drug eluting coatings on stent surfaces which include various pharmacologically active therapeutic agents on stents. Such coatings, however, can provide little actual control over the release kinetics of beneficial agents.
Control of the rate and uniformity of the drug elution of a stent is considered to be very important. It has also been found to be beneficial to provide a luminal stent surface having some surfaces with different drug effects than other surfaces. Furthermore, restenosis may not occur at the same rate or level in all regions of a vessel. For example, restenosis may not occur at the same rate or level in all regions of a bifurcated vessel. Therefore, it may be beneficial in the case of a vessel bifurcation to optimize the drug dosage in specific, high risk restenosis regions within a bifurcated lesion.
It has also been observed that higher drug concentration can occur in the center of the abluminal surfaces of the stent. This may be due to inhibition of normal intra mural transport due to the barrier presented by the stent itself, and the compression of the vessel wall behind the stent struts. This may also be due to more rapid protein deposition around the struts of the stent after implantation, particularly in the space between the lateral surface of the stent and the vessel wall.
There remains a need in the art for a stent system in which the drug dosage can be optimized in specific regions of the stent surface.
There remains a need in the art for a stent system in which the drug dosage can be optimized in specific, high risk restenosis regions within a bifurcated lesion.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.